Electroless copper plating compositions are in widespread use in metallization industries for depositing copper on various types of substrates. In the manufacture of printed wiring boards, for example, the electroless copper baths are used to deposit copper into through-holes and circuit paths as a base for subsequent electrolytic copper plating. Electroless copper plating also is used in the decorative plastics industry for deposition of copper onto non-conductive surfaces as a base for further plating of copper, nickel, gold, silver and other metals as required.
Electroless copper plating compositions often tend to spontaneously decompose after a certain period of time whether or not they are in active use. It is considered that small amounts of metallic copper nuclei generated in the plating compositions initiate a random deposition process, which inevitably decreases the overall stability of electroless copper plating composition and shortens the useful bath life. The metallic copper nuclei is formed by a disproportionation reaction of monovalent copper oxide (Cu2O), which is generated by incomplete reduction of divalent copper ion (Cu2±) because of poor stability of an electroless copper plating composition. Such decomposed electroless copper plating baths may result in poor quality deposited copper films with dark-colored appearance.
In order to solve the problem, many stabilizers for electroless copper plating baths were developed. See U.S. Pat. No. 3,257,215; U.S. Pat. No. 3,361,580; U.S. Pat. No. 3,649,308; U.S. Pat. No. 3,310,430; U.S. Pat. No. 3,095,309; U.S. Pat. No. 3,222,195; U.S. Pat. No. 3,392,035; U.S. Pat. No. 3,453,123; U.S. Pat. No. 3,903,907; U.S. Pat. No. 3,436,233; U.S. Pat. No. 3,790,392 and U.S. Pat. No. 3,804,638. However, some of the stabilizers disclosed in these patents cause other problems—such as low deposition rate of the electroless copper plating or poor copper deposited layers. Therefore, there remains a need for developing new stabilizers which prevent decomposition of the electroless copper plating bath and extend the bath life, without decreasing deposition rate and the quality of copper deposited layer.